Conventional interposer assemblies are mounted on substrates by pins extending from the assemblies through holes on the substrates or by positioning the interposers in alignment collars mounted on the substrates. The connections between the interposer assemblies and the substrates have limited lateral compliance. This compliance permits use of the interposer assemblies for connecting substrates which are laterally offset a small distance only and permits limited shifting of the substrates in response to lateral forces after the interposer assembly has been mounted on the substrates.
In many applications, interposer assemblies are needed to establish and maintain continuous electrical circuit paths between contact pads on substrates with increased lateral compliance between the substrates. Increased compliance is needed because of possible large substrate offset when the interposer assemblies are installed. The substrates may be offset by an amount greater than can be accommodated by the limited lateral compliance provided by conventional interposer assemblies. Increased compliance is also needed because after an interposer assembly is mounted between two substrates, the substrates may be subject to lateral forces. Lateral forces should not stress mounted interposer assemblies or be transmitted from one substrate through a mounted interposer assembly to another substrate.
One interposer assembly according to the invention includes a top plate, which is mounted on a top substrate, a bottom plate, which is mounted on a bottom substrate, a shift interface between the plates and a plurality of electrical circuit paths extending through the plates and across the interface to contact surfaces on noses at the top of the top plate and at the bottom of the bottom plate. The circuit paths provide continuous electrical connections between pads on the substrates. The top and bottom plates shift laterally along the interface to provide greater lateral compliance than in conventional interposer assemblies.
The top and bottom plates may be secured together by pins. Vertical pins may extend through passages in the plates. The pins permit limited lateral movement of the plates so that the interposer assembly can be mounted on misaligned substrates. The pins permit the interposer assembly plates to move laterally along the interface in response to lateral forces exerted on the substrates.
Another interposer assembly according to the invention includes top and bottom plates and a central circuit board plate located between the top and bottom plates. The top and bottom plates are mounted on the substrates. Contact passages extend through each top and bottom plate with contacts fitted in the passages. Contact surfaces are provided on noses at the upper and lower sides of the top and bottom plates. Opposed pairs of pads are provided on the top and bottom surfaces of the central circuit board plate with metal conductors extending across the plate between top and bottom pads. The contacts on the top and bottom plates engage the pads on the circuit board plate at pressure connections. The three plates are held together by pins fitted in holes in the plates. The pins permit controlled lateral shifting of the plates at two shift interfaces.
In the disclosed interposer assemblies, top and bottom plates are mounted on the substrates using collars or pins with the contacts in the top plate engaging pads on the top substrate and contacts in the bottom plate engaging pads on the bottom substrate. Continuous electrical circuit paths extend through the assemblies to connect opposed pads on the substrates. In the two-plate interposer assembly, single contacts may be positioned in passages in both plates and form continuous metal circuit paths. In the three-plate interposer assembly, the circuit paths include contacts located in passages in the top and bottom plates, pads and conductors on the central circuit board plate and pressure electrical connections between the inner ends of the contacts and the pads on the circuit board plate.
Interposer assemblies having three plates and two shift interfaces have greater compliance than two-plate, one shift interface interposer assemblies to permit mounting on misaligned substrates and lateral shift of the substrates without transmitting forces between the substrates after the assemblies have been mounted between the substrates. Additionally, the height of the interposer assembly can be easily and inexpensively altered by varying the thickness of the central circuit board plate. Top and bottom plates may be identical.
The invention also relates to an elongate strip metal contact useful in interposer assemblies for forming electrical connections between spaced contact pads with a small, single contact tip on each end of the contact located on the end of a bent up tab on or very close to the longitudinal axis of the contact. Providing a single small contact tip located on a tab bent up from the contact at or adjacent to the longitudinal axis of the contact provides high-pressure contact engagement with pads. The central location of the contact tip with respect to the width of the contact assures that loading forces exerted on the contact by engagement with a pad extends essentially along the longitudinal axis of the contact to reduce off-center forces and prevent the compressed contact from binding in the contact passages in the interposer plates. The location of a tip on each bent up tab close to or on the longitudinal axis of the contact assures resiliency of the contacts and provides high-pressure connections with the overlying and underlying pads.
The tips on the tabs are at the intersection of two rounded shear corners on the tab and are exceedingly small. The reduced size of the contact tips increases contact pressure to improve electrical connections between the tips and pads.